Systems for isolating and transplanting pancreatic islets

ABSTRACT

A microfluidic device can include an upstream passage, a sample passage, a bifurcating passage, and a combining passage. The upstream passage can be configured to provide a focusing stream. The sample passage can be configured to provide a sample stream. The bifurcating passage can include a specified bifurcating flow resistance. The combining passage can be configured to create a combined stream from the focusing stream and the sample stream, where the focusing stream can direct the sample stream away from the upstream passage and toward the bifurcating passage. A first portion of the combined stream can be discharged through the bifurcating passage. The main discharge can be configured to discharge a second portion of the combined stream. The main discharge can include a main discharge resistance that is selectable to vary the main discharge resistance relative to the bifurcating flow resistance.

CLAIM OF PRIORITY

This patent application claims the benefit of priority to Swami, U.S.Provisional Patent Application Ser. No. 62/324,938, entitled “SYSTEMSAND METHODS FOR ISOLATING AND TRANSPLANTING PANCREATIC ISLETS,” filed onApr. 20, 2016, which is hereby incorporated by reference herein in itsentirety.

BACKGROUND

Type 1 Diabetes (T1D) is a major cause of morbidity and mortalityworldwide. In 2012, an estimated $245 billion dollars was spent treatingand managing diabetes in the United States. This constitutes a 40%increase in cost related to the disease from five years earlier with anestimated $174 billion spent in 2007. The costs associated with T1Dtreatment and management are typically higher on a per case basis thanthose due to Type 2 Diabetes (T2D). In many cases, long term managementof T1D is achieved through lifelong exogenous insulin administrationused to synthetically regulate blood glucose and achieve energyhomeostasis. However, while this therapy may generally prevent or evenreverse long-term T1D complications in some patients, it often fails toreplicate the necessary sensitivity towards glucose regulation, asachieved by a healthy pancreatic endocrine function, thereby leavingsubjects vulnerable to severe episodes of hypoglycemia and hyperglycemicunawareness.

While no long-term cure exists for T1D, transplantation of pancreaticislet of Langerhans has demonstrated the ability to restore a patient'sendocrine function for short periods, typically up to five years.However, many current methods for isolating pancreatic islets result inonly partial sample purification and substantial loss of transplantmaterial.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, which are not necessarily drawn to scale, like numeralsmay describe similar components in different views. Like numerals havingdifferent letter suffixes may represent different instances of similarcomponents. The drawings illustrate generally, by way of example, butnot by way of limitation, various embodiments discussed in the presentdocument.

FIG. 1 illustrates a schematic view of a process, in accordance with atleast one example of the present disclosure.

FIG. 2 illustrates a schematic view of a system, in accordance with atleast one example of the present disclosure.

FIG. 3 illustrates a schematic view of another system, in accordancewith at least one example of the present disclosure.

FIG. 4 illustrates a schematic view of a microfluidic device, inaccordance with at least one example of the present disclosure.

FIG. 5 illustrates a schematic view of a microfluidic device, inaccordance with at least one example of the present disclosure.

FIG. 6 illustrates a schematic view of a microfluidic device, inaccordance with at least one example of the present disclosure.

FIG. 7 illustrates a schematic view of a microfluidic device, inaccordance with at least one example of the present disclosure.

FIG. 8 illustrates a schematic view of a microfluidic device, inaccordance with at least one example of the present disclosure.

FIG. 9 illustrates a view of a microfluidic device, in accordance withat least one example of the present disclosure.

FIGS. 10A-10E illustrate operations of a microfluidic device, inaccordance with at least one example of the present disclosure.

FIGS. 11A-11E illustrate operations of a microfluidic device, inaccordance with at least one example of the present disclosure.

FIGS. 12A-12F illustrate operations of a microfluidic device, inaccordance with at least one example of the present disclosure.

FIG. 13 illustrates a schematic view of a microfluidic system, inaccordance with at least one example of the present disclosure.

FIG. 14A illustrates an image of islet particles, in accordance with atleast one example of the present disclosure.

FIG. 14B illustrates an image of islet particle distribution, inaccordance with at least one example of the present disclosure.

FIG. 15 illustrates an image of a bio-printing system, in accordancewith at least one example of the present disclosure.

DETAILED DESCRIPTION

The inventors have recognized, among other things, that while nolong-term cure exists for T1D, transplantation of pancreatic islet ofLangerhans has demonstrated the ability to restore a patient's endocrinefunction for short periods, typically up to five years. However, somecurrent methods for isolating pancreatic islets result in only partialsample purification and substantial loss of transplant material. Onaverage, there is estimated to be around 2 million pancreatic isletswithin a healthy set of human pancreas. Some currently used isolationtechniques result in an islet yield of around 800,000 useable islets,suggesting a potential loss of over 50% of transplantable isletmaterial. Because this isolation method uses a density gradient toseparate islet material from contaminant acinar tissue, the separatedislets are not selected based on their functional quality or beta cellviability, which are of paramount importance within their downstreamtransplant application. On one hand, the discarded samples from thismethod can include large numbers of viable islets with high membrane andmitochondrial integrity that present high revascularization potentialafter transplantation, but are discarded due to the difficulty inseparating them from acinar tissue. On the other hand, the collectedsample exhibits a high degree of variability in islet quality due tosize-based differences in islet functionality and due to presence of asignificant proportion (˜30%) of acinar tissue, thereby causing aninvasive transplant procedure due to its higher volume, as well asenhancing its susceptibility to immune cell invasion. Together, theseproblems substantially increase the islet transplant costs andexacerbate immune rejection.

In some examples, the present subject matter can provide a solution tothis problem, such as by using a microfluidic approach that utilizes themicroscale differences in the deformability and hydrodynamic flowstreamlines to cause selective flow displacements of particular cellaggregates for enabling:

(i) separation of islets versus acinar tissue;

(ii) separation of small versus large islets;

(iii) separation of cell aggregates based on viability; and

(iv) construction of transplants with spatially patterned architecturesof cell aggregates.

Disclosed herein are systems, compositions, and methods for separationmodalities under crossflow and hydrodynamic displacement and two-cycleseparation that allow for collection of islets integration with thecollection systems with three-dimensional (3D) bio-printing. In someexamples, these methodologies can be useful for isolating high valueislets and for construction of transplants with patterned architectures.

This overview is intended to provide an overview of subject matter ofthe present patent application. It is not intended to provide anexclusive or exhaustive explanation of the present subject matter. Thedetailed description is included to provide further information aboutthe present patent application.

Microfluidic Devices

Microfluidic separation methods rely on selective particle displacementsunder the well-determined laminar flow streamlines that exist withinmicrofluidic systems due to their low dimensionless Reynolds number(ratio of inertial and viscous forces under flow, as per Eq. 1) andStokes number (factor describing how quickly a particle will react tochanges in the carrier stream, as per Eq. 2):

Re=(U*D _(h))/ν   Equation 1

Here, U is the average fluid velocity, D is the characteristic dimensionof a channel or obstacle, and ν is the kinetic viscosity (10⁻⁶ m/s² forwater). Laminar flow occurs in cases wherein the Re drops below athreshold value (Re_(trans)) for a given circumstance, with a Re_(trans)range of 1,000 to 2,000 for fluid flowing through a channel and 65 to100 for a fluid flowing around an object. The Stokes number of a pipecan be given by:

St=((P _(p) *a ²)/18*μ)/(D _(h) /U)   Equation 2

Here, a is the diameter of the particle, P_(p) is the density of theparticle, D_(h) is the hydraulic diameter, and μ is the viscosity of thecarrier fluid. In cases of low stokes numbers the particle will reactrapidly to changes in its carrier stream. In the case of flows throughmicrofluidic systems Reynolds numbers are typically extremely low due tothe small geometric dimensions of the channels, usually ranging between1 and 10⁻⁴. Similarly, in the case of microparticles, such as cells orother bio-colloids, the Stokes numbers are also typically low. In caseswhere the Re of the carrier fluid flow and the St of the particle aresmall, the trajectory of a particle will follow the streamline of theflow passing through its center of gravity. Utilizing these phenomena,three broad mechanisms of separation are available. These areseparations utilizing: (i) particle to wall interactions, (ii) particleto flow interactions, and (iii) particle to force field interactions.Methods utilizing the particle to wall mechanism rely on interactionwith rigid structures within the microfluidic device.

These interactions may be used to exert a deterministic force on aparticle, thereby achieving separation through selective particledisplacement, based on parameters such as particle size or deformabilityso that particles can be separated and or collected, as discussed below.

FIG. 1 illustrates a schematic view of process 100, in accordance withat least one example of the present disclosure. FIG. 1 shows centrifuge102, low density waste 104, low density low purity islets 106, middensity high purity islets 108, high density low purity islets 110, andhigh density acinar waste 112.

Centrifuge 102 can be a device configured to separate particles ofvarying density. In operation of some examples, tissue samples can beloaded into a process bag centrifuge 102 and spun, for example at 3000rpm for 5 minutes. During this time, centrifugal force can separatedigested aggregates along a density gradient, as shown in FIG. 1.

As a result, denser acinar material can move to the outer regions of theprocess bag, as indicated by reference numeral 112 and the lower densityislet material can move towards the center of the process bag, asindicated by reference numeral 104. The contents of the process bag canthen be further separated into 12 fractions, for example of 25milliliters, where medium size and density particles can be collected insections 106, 108, 110. The remaining volume in the process bag afterseparation can be discarded. The collected fractions can be evaluatedfor islet purity and volume of packed tissue. In some examples,collected fractions of similar purity can be combined into threedifferent groups of varying purity levels: high (fractions above 80%purity); medium (80%-50%); and low (50%-30%), while the discarded samplecontains less than 20% purity. The collected fractions can be used inthe methods and systems described herein.

FIG. 2 illustrates a schematic view of system 200, in accordance with atleast one example of the present disclosure. System 200 can include highpressure source 202, media reservoir 204, flow switch 206, samplereservoir 208, pump 210, sample injection 212, flow switch 214, testdevice 216, multiplexer 218, and waste reservoir 220. Test device 216can include channels 222, 224, 225, and 228. Test channel 228 caninclude media inlet 230, sample inlet 232, focused portion 234, whichshows channel 228 in two conditions. Channel 228 can include restriction236, which can receive flows 228A and 228B. Flow 228A can carry particle240 and flow 228B can carry particle 242.

High pressure source 202 can be a pump or other pressurization deviceconfigured to pressurize media reservoir 204. Flow switch 206 can be anon/off flow switch, such as a flow control valve, such as a butterflycontrol valve, piezo-electric switch, rotary valve, or a modulating ballcontrol valve. Flow switch 206 can be connected to media inlet 230. Pump216 can be a pump or other pressurization device configured topressurize sample injection 212 via flow switch 214. Sample reservoir208 can be a container or reservoir of sample tissue injectable intosample injection 212 via an independent pump or via pump 210 (forexample using an aspirator arrangement). Sample injection 212 can beconnected to sample inlet 232.

Testing device 216 can include media inlet 230, which can connect to aninlet orthogonal to sample inlet, such that a sample stream isdistributed across a header or manifold orthogonally to media inlet 230.Channels 222-228 can each be connected to the manifold to receive acombination of the media stream and the sample stream. A discharge ofeach of channels 222-228 can be individually connected to multiplexer218, which can connect to waste reservoir 220.

Each of channels 222-228 can each have a size or diameter, such as 400micrometers, in some examples, and each of channels 222-228 can includeone or more restrictions. As shown in focused portion 234, channel 228can include restriction 236, which can have a size or dimeter, forexample, of 80 micrometers. In some examples restriction 236 can beapproximately 80% of a diameter of acinar material. In other examples,restriction 236 can be of other sizes, such as 10 micrometers to 200micrometers. For example, the restrictions of channel 222 can be 60micrometers, the restrictions of channel 224 can be 70 micrometers, andthe restrictions of channel 226 can be 90 micrometers. In one example,an optimal device was determined to be a channel with 400 micrometers ofwidth and 350 micrometers of height, with a restriction of 80micrometers that represents 80% of a smallest islet diameter in alateral dimension and 150% of a largest islet diameter in a verticaldimension, thereby ensuring no more than 75% occlusion in therestriction.

In operation of some examples, a sample stream can be delivered tosample inlet 232 and a media stream can be delivered to media inlet 230to direct the sample stream flow. Which of channels 222-228 is used toreceive a stream is determined by multiplexer 218, which can act as amulti-way switch to select which of channels 222-228 is open. In oneexample, such as shown in focused portion 234, stream 238A can carry adeformable particle, such as an acinar 240, which can deform to fitthrough restriction 236. As also shown in focused portion 234, islet 242cannot fit through restriction 236. This can be an indication that thesize of restriction 236 is a good size to perform separation ofdeformable acinar particles from non-deformable islets.

In some examples, system 200 can be used to determine an idealrestriction size for use in a microfluidic separation system thatseparates islets and acinar material based on deformability, in someexamples. In some examples, system 200 can be used to determine arestriction size that is specific to the islet and acinar tissues of aspecific donor pancreas.

FIG. 3 illustrates a schematic view of system 300, in accordance with atleast one example of the present disclosure. System 300 can includemicrofluidic device 302, main discharge multiplexer 304, bifurcatingmultiplexer 306, high resistance source 308, waste reservoir 310, lowresistance source 312, islet reservoir 314, low resistance source 316,high resistance source 318, and acinar waste reservoir 320. Microfluidicdevice 302 can include sample passage 322, upstream passage 324,combining passage 326, main discharge 328, and bifurcating passage 330.System 300 can also include main discharge sensor 301, bifurcatingpassage sensor 303, and controller 305.

Main discharge multiplexer 304 and bifurcating multiplexer 306 can bemultiplexers or other switching devices configured to selectively switchthe connection of an inlet to multiple outlets. In some examples,multiplexer 304 and bifurcating multiplexer 306 can include fast-actingpiezo-electric switches for switching between connections of theirrespective inputs to different respective outputs. Main dischargemultiplexer 304 can be connected to a downstream side of main discharge328. A downstream side of main discharge multiplexer 304 can beconnected to high resistance source 308 and low resistance source 312.High resistance source 308 can be connected to waste reservoir 310 andlow resistance source 312 can be connected to islet reservoir 314.

Bifurcating multiplexer 306 can be connected in parallel to a downstreamside of bifurcating passage 330. A downstream side of bifurcatingmultiplexer 306 can be connected in parallel to low resistance source316 and high resistance source 318. Each of low resistance source 316and high resistance source 318 can be connected to acinar wastereservoir 320.

Each of high resistance source 308 and high resistance source 318 can bea source used to impose a high resistance or pressure drop therethrough.High resistance sources 308 and 318 can be adjustable (for examplevalves) in some examples, and can be non-adjustable pressure-inducingdevices in other examples, such as permeable membranes and linerestrictions. Low resistance source 312 and low resistance source 316can also be adjustable valves in some examples and can be non-adjustabledevices in other examples. In some examples, low resistance source canbe an open line.

Waste reservoir 310, islet reservoir 314, and acinar waste reservoir 320can be reservoirs configured to receive and store fluid, such as flasks,bottles, beakers, hermetic containers, and the like.

Microfluidic device can include sample passage 322 configured to receivea sample stream and delver the sample stream to combining passage 326,which can be downstream of sample passage 322. Upstream passage 324 canbe configured to receive a focusing stream and provide the focusingstream to combining passage 326, which can be downstream of upstreampassage. Focusing stream can direct the sample stream towardsbifurcating passage 330, as discussed further below. The focusing streamand sample stream combine in combining passage 326 to form a combinedstream. Main discharge 328 can be configured to discharge a portion thecombined stream, and bifurcating passage 330 can be configured todischarge another portion of the combined stream, as discussed furtherbelow.

Main discharge sensor 301 and bifurcating passage sensor 303 can besensors configured to measure conditions of main discharge 328 andbifurcating passage 330, respectively, and produce signals based on themeasured conditions. Each of main discharge sensor 301 and bifurcatingpassage sensor 305 can be in communication with controller 305. Maindischarge sensor 301 can be coupled to, and in some cases in fluidcommunication with, main discharge 328 or a header or line downstreamthereof. Bifurcating passage sensor 303 can be coupled to, and in somecases in fluid communication with, bifurcating passage 330 or a headeror line downstream thereof.

Controller 305 can be a computing device, such as a handheld computer,for example, a smart phone, a tablet, a laptop, a desktop computer, orany other computing device including a processor and wired or wirelesscommunication capabilities. Controller 305 can include or can beconnected to a user interface and/or an input device. In some examples,a user interface can be a monitor, keyboard, and mouse in one example.In other examples, the user interface can be a touch screen display. Inyet another example, the user interface can provide only a display forcontroller 305. Controller 305 can be connected to and in communicationwith main discharge sensor 301, bifurcating passage sensor 305, maindischarge multiplexer 304, and bifurcating multiplexer 306.

Controller 305 can include machine readable medium. The terms “machinereadable medium” may include any medium that is capable of storing,encoding, or carrying instructions for execution by the device and thatcause the device to perform any one or more of the techniques of thepresent disclosure, or that is capable of storing, encoding or carryingdata structures used by or associated with such instructions.Non-limiting machine readable medium examples may include solid-statememories, and optical and magnetic media. Specific examples of machinereadable media may include: non-volatile memory, such as semiconductormemory devices (e.g., Electrically Programmable Read-Only Memory(EPROM), Electrically Erasable Programmable Read-Only Memory (EEPROM))and flash memory devices; magnetic disks, such as internal hard disksand removable disks; magneto-optical disks; and CD-ROM and DVD-ROMdisks.

In operation of some examples, individual pumps (such as those shown inFIG. 2) can be used to pressurize and deliver sample stream and focusingstream to sample passage 322 and upstream passage 324, respectively fortwo-cycle separation, as discussed further below in FIGS. 4 and 5.During the separation cycle of the two-cycle separation, main dischargemultiplexer 304 can connect main discharge 328 to high resistance source308 and bifurcating passage multiplexer can connect bifurcating passage330 to low resistance source 316 to create a middle (or mid) resistanceat bifurcating passage 330. In this conditions, as described in FIGS. 3and 4 below, bifurcating passage 330 can receive deformable particlesfrom the sample stream, which can be acinar in some examples, while maindischarge 328 can receive a large portion of the combined flow. Thedeformable particles can pass through bifurcating passage 330,multiplexer 306, low resistance source 316, and be deposited into acinarwaste reservoir 320. The combined flow can pass through main discharge328, main discharge multiplexer 304, high resistance source 308, and canbe deposited into waste reservoir 310.

When a non-deformable particle (such as an islet) clogs or partiallyclogs bifurcating passage 330, a fluid property of the portion of flowdischarged by bifurcating passage 330 will be altered. For example, aflow rate through bifurcating passage 330 can lower and a pressurewithin bifurcating passage (and upstream of bifurcating multiplexer 306)can rise. In other examples, the fluid can change in other ways. Anychange can be detected by bifurcating passage sensor 303. For example,bifurcating passage can detect a pressure drop in the flow frombifurcating passage 330. Bifurcating passage 330 can then alter itssignal sent to controller 305. Controller 305 can determine, based on areduced pressure signal (or other changed condition) that anon-deformable particle is partially clogging bifurcating passage 330.Controller 305 can then send a signal to main discharge multiplexer 304to switch to low resistance source 312 and a signal to bifurcatingmultiplexer 306 to switch to high resistance source 318. This change inresistance can cause the non-deformable particle or particles (such asislets) clogging bifurcating passage 330 to enter main discharge 328,clearing the clog. The unclogged islets or non-deformable particles canenter main discharge 328, pass through main discharge multiplexer 304,pass through low resistance source 312 and into islet reservoir 314.

After the clog has been cleared, a change in conditions can be detectedby one or both of main discharge sensor 301 and bifurcating passagesensor 303. Controller 305 can use these signals to determine thatbifurcating passage 330 is clear and can then send a signal to maindischarge multiplexer 304 to connect again to high resistance source 308and a signal to bifurcating passage multiplexer 306 to connect again tolow resistance 316. In some examples, controller 305 can wait anincrement of time before sending the signals to switch the multiplexers.

This process can be repeated many times to continuously separatedeformable acinar particles from non-deformable islet particles. Byrepeating multiple cycles of two-cycle separation islets can beseparated from acinar tissue, providing a high concentration of isletcells. By collecting higher concentration of islet cells, the number ofdonor samples required can be reduced. Further, by removing acinartissue, rejection rates of transplant recipients can be lowered.

FIG. 4 illustrates a schematic view of microfluidic device 302, inaccordance with at least one example of the present disclosure.Microfluidic device 302 can include sample passage 322, upstream passage324, combining passage 326, main discharge 328, and bifurcating passage330. Also shown in FIG. 4 are islets 332, acinar 334, sample stream sa,focusing stream f, combined stream m, discharge stream d, selectedstream sl, pinch width w_(a), selection width w_(s), and bifurcatingpassage width w_(b).

Microfluidic device 302 of FIG. 4 can be consistent with the descriptionof FIG. 3; however, FIG. 4 shows additional details of the operation ofmicrofluidic device 302. FIG. 4 also shows that upstream passage isoffset from orthogonal relative to main passage 322. In some examples,the angle of upstream passage relative to main passage can be between 5degrees and 85 degrees. In other examples, the angle can be between 30degrees and 60 degrees. FIG. 4 also shows bifurcating width w_(b), whichcan be smaller than a width of main discharge 330.

In operation of some examples, sample stream sa can be provided bysample passage 322 and can include acinar particles 334 and islets 332.As discussed above, acinar particles 334 can be significantly moredeformable than islet particles. Focusing stream f (which can be anon-volatile solution) can be injected into microfluidic device byupstream passage 324 at an angle relative to sample passage 322 andtherefore sample stream sa. Focusing stream f can interact with samplestream sa, creating pinch width w_(a), which can be a width at whichsample stream sa is forced to pass through. Because microfluidic device302 is of micro dimensions (for example, combining width can be 1000micrometers, in some examples), the Reynolds numbers of focusing flow fand sample stream sa can be laminar, preventing sample stream sa andfocusing flow f from creating an eddy current or turbulent flow withincombining passage 326.

As sample stream sa and focusing flow f interact, they can createcombined stream m within combining passage 326, while acinar 334 andislets 332 are forced towards bifurcating passage 330. As shown in FIG.3, main discharge 328 can be connected to a high resistance sourcecreating a high flow resistance (HIGH of FIG. 4) at main discharge 328and bifurcating passage 330 can be connected to a low resistance sourcecreating a mid-resistance (MID of FIG. 4) at bifurcating passage 330.The ratio of the resistance of the main discharge to the resistance ofthe bifurcating passage can dictate selection width w_(s), whereselection width w_(s) can dictate a flow path taken by particles ofcombined stream m. For example, when the ratio of resistances creates aselection width w_(s) significantly large, bifurcating path 330 canreceive acinar 334. In this condition bifurcating path 330 can alsoreceive islets 332. However, because islets 332 do not deform theycannot travel through bifurcating passage 330, which can have a width ofapproximately 80% of a width of acinar 334 and islets 332. Becauseacinar 334 can deform, acinar 334 can travel into bifurcating passage330. Because islets do not deform, they can be held by at an opening ofbifurcating passage 330 caused by pressure differential. The secondportion of the two-cycle separation is discussed in FIG. 5 below.

FIG. 5 illustrates a schematic view of microfluidic device 302, inaccordance with at least one example of the present disclosure.Microfluidic device 302 can include sample passage 322, upstream passage324, combining passage 326, main discharge 328, and bifurcating passage330. Also shown in FIG. 4 are islets 332, sample stream sa, focusingstream f, combined stream m, discharge stream d, selected stream sl,pinch width w_(a), selection width w_(s), and bifurcating passage widthw_(b).

Microfluidic device 302 of FIG. 5 can be consistent with the descriptionof FIG. 4, except that FIG. 5 shows the sample collection phase of thetwo-cycle separation process, where main discharge 328 is connected to alow pressure source to create a low flow resistance at main discharge328 (shown as LOW in FIG. 5) and bifurcating passage 330 is connected toa high resistance source to create a high flow resistance in bifurcatingpassage 330 (shown as HIGH in FIG. 5). As a result, the selection widthw_(s) can be significantly smaller than in FIG. 4, causing a reducedselected stream sl. This arrangement can also cause islets trapped at anopening of bifurcating passage 330 (as shown in FIG. 4) to release andexit microfluidic device 302 through main discharge 328 so that isletcells can be collected, as illustrated in FIG. 5 by islet 332 enteringmain discharge 328.

As discussed above, the two-cycle separation process shown in FIGS. 4and 5 can be repeated in small increments of time to collect a highquantity of islet cells without causing damage to the islets. Thoughislets are not deformable, islets have a relatively low Young's modulusinter-cellular matrix. This means islets subjected to high forces whileclogging the opening of bifurcating passage 328 can cause islets tobreak apart, making pressure and timing critical to avoid separation. Insome examples, the cycle can switch quickly, such as every one second,in some examples, to avoid separation of islet cells. Further the shapeof bifurcating passage 328 can have an oval or other shape cross sectionthat avoids complete clogging of bifurcating passage 328 by islets 332.This can help to reduce pressure and therefore forces applied to islets332, lowering the likelihood of damage caused to the islets by forcesapplied by the opening of bifurcating passage 328 onto the islets.

FIG. 6 illustrates a schematic view of microfluidic device 600, inaccordance with at least one example of the present disclosure.Microfluidic device 600 can include sample passage 622, upstreampassages 624 a-624 n, combining passage 626, main discharge 628, andbifurcating passages 630 a-630 n. Also shown in FIG. 4 are sample streamsa, focusing stream f, combined stream m, discharge stream d, selectedstream sl, pinch width w_(a), selection width w_(s), and bifurcatingpassage width w_(b).

Microfluidic device 600 can be similar to microfluidic device 302described above, except that microfluidic device 600 can include aplurality of upstream passages 624 a-624 n and a plurality ofbifurcating passages 630 a-630 n. Each of upstream passages 624 a-624 ncan be offset from an orthogonal angle from sample passage 622. Asdiscussed with respected to microfluidic device 302 above, each ofupstream passages 624 a-624 n can have an angle with respect to samplepassage 622 between 20 degrees and 70 degrees, in some examples. Each ofupstream passages 624 a-624 n can be immediately upstream of one ofbifurcating passages 630 a-630 n. For example, upstream passage 624 acan be upstream of bifurcating passage 630 a, but upstream passage 624 bcan be downstream of bifurcating passage 630 a, as shown in FIG. 7.

Each of upstream passages 624 a-624 n can be configured to deliverfocusing stream f to align sample stream sa with selection width w_(s),similar to microfluidic device 302. However, in microfluidic device 602,each of upstream passages 624 a-624 n realigns sample stream sa and/orcombined stream m prior to each of bifurcating passages 630 a-630 n.Accordingly, each of upstream passages 624 a-624 n provide focusingstream f at a flow rate required to perform alignment of sample streamsa and to make up for a flowrate of selected stream sl dischargedthrough each of bifurcating passages 630 a-630 n. Each of bifurcatingpassages 630 a-630 n can be configured and sized to receive deformableacinar while not accepting viable islets of a similar size to theacinar, as described with respect to FIGS. 3-5 above.

In operation of some examples, microfluidic device 600 can be cycled ina two-cycle separation process as described above with respect to FIGS.3-5. Except that, because microfluidic device 600 contains manybifurcation passages, several or many acinar and islets can be collectedduring each two-cycle separation cycle, increasing collection speed andefficiency.

FIG. 7 illustrates a schematic view of microfluidic device 700, inaccordance with at least one example of the present disclosure.Microfluidic device 700 can include sample passage 722, upstream passage724, combining passage 726, main discharge 728, and bifurcating passage730. Also shown in FIG. 7 are islets 732, acinar 734, sample stream sa,focusing stream f, combined stream m, discharge stream d, selectedstream sl, pinch width w_(a), selection width w_(s), and bifurcatingpassage width w_(b).

Microfluidic device 700 can be consistent with the description ofmicrofluidic device 302 of FIGS. 3-5 above. However, FIG. 7 illustratesan application of a middle pressure source the each of main discharge728 and bifurcating passage 730 to create a mid flow resistance at eachof main discharge 728 and bifurcating passage 728 (shown in FIG. 7 asMID and MID).

In this configuration, deformable cells, such as acinar 734 can beselected through bifurcating passage 730. But, because the resistance inmain discharge 728 is about the same as bifurcating passage 730, islets732 can be discharged through main discharge 728, as shown in FIG. 7.This process can accomplish separation and collection of acinar andislets without a two-cycle process, which can save time and energy.

FIG. 8 illustrates a schematic view of microfluidic device 800, inaccordance with at least one example of the present disclosure. FIG. 9illustrates a schematic view of microfluidic device 800, in accordancewith at least one example of the present disclosure. FIGS. 8 and 9 arediscussed below concurrently.

Microfluidic device 800 can include sample passage 822, upstream passage824, combining passage 826, main discharge 828, and bifurcating passage830. Also shown in FIG. 8 are small cells 832, and large cells 834,sample stream sa (838 in FIG. 9), focusing stream f (836 in FIG. 9),combined stream m, discharge stream d, selected stream sl, largeparticle center of gravity 840 (only shown in FIG. 9), small particlecenter of gravity 842 (only shown in FIG. 9), pinch width w_(a),selection width w_(s), and bifurcating passage width w_(b).

In FIG. 8, a high flow rate focusing stream f can pinch sample stream sato a width w_(a). Sample stream sa can include small (r<W_(a)) 832 andlarge (r>W_(a)) 834 cell aggregates. Because, large cell center ofgravity 840 is further away from the channel sidewall than those ofsmaller aggregates 832, small cell center of gravity 842 can be withinselection width w_(s) and large particle center of gravity 840 can beoutside of selection width w_(s). Resistance of bifurcating passage 830can be high due to its smaller size (shown in FIG. 8 as HIGH) to that ofmain discharge 828 due to its larger size (shown in FIG. 8 as LOW),which can determine the width (w_(s)) over which bifurcating passage 830can select aggregates. Though FIGS. 8 and 9 show a particle sizedifference, a size difference is not necessary for hydrodynamicfiltration. Differences in center of gravity can be sufficient toachieve separation when flow rates/resistances are correctly selected.

In some examples, adjustment of the resistances can enable a smallenough w_(s) for selecting smaller particles, such as small cells 832.This process can be referred to as hydrodynamic separation, where arelatively large difference in the flow rates of focusing stream f andsample stream sa can ensure a small enough w_(a) for driving all cellaggregates towards the channel sidewall near bifurcating passage 330.This coupled with low resistance at main discharge 828 and highresistance at bifurcating passage 830 can enable appropriate w_(s) forselection of cells based on size. This process can be used to separatecells of different sizes, such as acinar, islets, and small, medium, andlarge islets.

Further, because microfluidic devices 302, 700, and 800 can be the samemicrofluidic device, a hydrodynamic mode for separation based on sizedifferences (such as shown in FIG. 8) can be performed on the samemicrofluidic device as two-cycle selection (such as shown in FIGS. 4 and5) and cross-flow separation (such as shown in FIG. 7), by simplymodulating input flow rates and outlet flow resistances by usingmultiplexing flow switches (such as main discharge multiplexer 304 andbifurcating passage multiplexer 306 of FIG. 3), without any alterationto channel dimensions or design of the microfluidic device.

FIGS. 10A-10E illustrate operations of microfluidic device 1000, inaccordance with at least one example of the present disclosure.Microfluidic device can include sample passage 1022, upstream passages1024 a-1024 n, bifurcating passages 1030 a-1030 n, and discharge passage1028. Also shown in FIGS. 10A-10E are acinar and islets.

FIGS. 10A-10E show a time lapse of acinar and islets interacting withmicrofluidic device 1000. As shown in FIG. 10A, acinar can enterbifurcating passage 1030 a and islets can engage 1030 n during aseparation cycle of two-cycle separation. The deformable structure ofthe acinar tissue causes it transferred into bifurcating passage 1030A(as shown in FIG. 10B0 of smaller size due to the lower flow resistanceof bifurcating passage 1030 a. Islets, on the other hand, can becometrapped by bifurcating passages due to non-deformability, as shown inFIGS. 10B and 10C. Acinar can continue through bifurcating passage 1030a, as shown in FIG. 10B. As shown in FIG. 10C, additional acinar canengage bifurcating passage 1030 a, as sample passage continues toprovide a sample stream during the separation cycle.

Then, the resistances can be altered (as described in FIGS. 3-5 above)so that the resistance of main discharge 1028 is lower than theresistance of bifurcating passages 1030 a-1030 n, causing the trappedislet to release from bifurcating passage 1030 n (as shown in FIG. 10D)where the islet can continue through main discharge 1028 and becollected downstream, leaving microfluidic device 1000 clear (as shownin FIG. 10E). This cycle can be repeated to separate and collect acinarand islets.

FIGS. 11A-11B illustrate operations of microfluidic device 1100, inaccordance with at least one example of the present disclosure.Microfluidic device 1100 can include sample passage 1122, upstreampassages 1124 a-1124 n, bifurcating passages 1130 a-1130 n, anddischarge passage 1128. Also shown in FIGS. 11A-11E are acinar andislets.

Collected samples from density gradient methods, such as shown in FIG.1, can include non-viable islets, which can exacerbate immune rejectionissues if included in transplanted material. Because gradual loss ofviability of islets causes the islets to become more deformable, lowviability islets can be separated from high viability islets using themicrofluidic devices discussed above. FIG. 11A shows islet samplestogether with acinar tissue. As shown in FIG. 11B islet samples start toexhibit the systematic ability to deform after approximately 75 hours ofharvesting, as FIGS. 11B-11D shows islets deforming into and passingthrough bifurcating passage 1130 until only acinar remains as shown inFIG. 11E. This can be achieved using either two-cycle separationdescribed with respect to FIGS. 3-5 or under the microfluidic crossflowmode described with respect to FIG. 7.

FIGS. 12A-12F illustrate operations of microfluidic device 1200, inaccordance with at least one example of the present disclosure.Microfluidic device 1200 can include sample passage 1222, upstreampassages 1224 a-1224 n, bifurcating passages 1230 a-1230 n, anddischarge passage 1228. Also shown in FIGS. 12A-12E are small highdensity islets 1232 and large islets 1234.

The collected sample from the density gradient based separation method,such as the method of FIG. 1, can provide a high degree of variabilityin islet size. Islets of smaller size are known to be better suited fortransplantation versus large islet, making smaller and denser isletsmore desirable. Separation of small and large islets can be achieved byusing the differences in flow streamlines for aggregates of differingsize under microfluidic hydrodynamic flow, as explained in FIGS. 8 and9. As shown in FIGS. 12A-12C, small islets can be transported downbifurcating passages 1230 a-1230 n, while larger particles can bedischarged through main discharge, as shown in FIGS. 12D-12F.

FIG. 13 illustrates a schematic view of microfluidic system 1300, inaccordance with at least one example of the present disclosure. System1300 can include sample reservoir 1302, which can include viable islets,non-viable islets, and acinar tissue (also shown throughout system1300). System 1300 can also include first sorting stage 1304, secondsorting stage 1306, large waste reservoir 1308, large collectionreservoir 1310, third sorting stage 1312, fourth sorting stage 1314,medium waste reservoir 1316, medium collection reservoir 1318, fifthsorting stage 1320, small acinar waste reservoir 1322, sixth sortingstage 1324, small waste reservoir 1326, and small collection reservoir1328.

In one example, first sorting stage 1307 can be configured to performhydrodynamic filtration (such as shown with respect to FIGS. 8 and 9above) to separate large particles from medium particles and smallparticles, where first sorting stage 1304 can include a first stagefirst discharge and a first stage second discharge. Second sorting stage1306 can be connected to the first stage first discharge. Second sortingstage 1306 can be configured to perform two-cycle separation (such as isdescribed in FIGS. 3-5, for example) to separate deformable largeparticles from non-deformable large particles. Waste reservoir 1908 cancollect non-viable islets and collection reservoir 1310 can collectviable islets.

Third sorting stage 1312 can be connected to first stage seconddischarge. Third sorting stage 1312 can be configured to performhydrodynamic filtration to separate medium particles from smallparticles. Third sorting stage 1312 can include a third stage firstdischarge and a third stage second discharge. Fourth sorting stage 1314can be connected to the third stage first discharge. Fourth sortingstage 1314 can be configured to perform two-cycle separation to separatedeformable medium particles from non-deformable medium particles. Thedeformable, non-viable islets can be collected in waste reservoir 1316and the viable islets can be collected in collection reservoir 1318.

Fifth sorting stage 1320 can be connected to the third stage seconddischarge. Fifth sorting stage 1320 can be configured to performcrossflow filtration (such as is shown in FIG. 7 above) to separatedeformable small particles from non-deformable small particles. Fifthsorting stage 1320 can include a fifth stage discharge and can deliveracinar waste to acinar waste reservoir 1322. Sixth sorting stage 1324can be connected to the fifth stage second discharge. Sixth sortingstage 1324 can be configured to perform two-cycle filtration to separatefirst non-deformable small particles from second non-deformable smallparticles. Though first through sixth stages are shown and discussed asperforming specific processes, each stage can be configured to performother processes to achieve different separation profiles. Similarly,though system 1300 is shown as having six separate systems or processes,less, or more individual systems or processes can be used to achieve thesame separation results, as the microfluidic devices used to perform theprocesses, as discussed above, can be used interchangeably, or toperform any of the three processes discussed herein.

Using these systems, system 1300 can separate small, medium, and largeviable islets from small, medium, and large non-viable islets, and canseparate acinar. Small, medium, and large viable islets can then becollected and used for transplant. By removing non-viable islets andacinar, transplant rejection can be reduced.

FIG. 14A illustrates an image of islet particles, in accordance with atleast one example of the present disclosure. FIG. 14B illustrates animage of islet particle distribution, in accordance with at least oneexample of the present disclosure. FIGS. 14A and 14B are discussedconcurrently.

A number of studies have established that while the number of islets perpancreas varies in proportion to the body weight of the mammal, anoptimal size distribution may be needed to support intercellularcoupling for stable synchronization of insulin secretion, becauseeffectively coupled β-cells can produce the necessary bursting actionpotentials, whereas single cells can only generate spiking actionpotentials. Some islets can be arranged in architectures of cellaggregates ranging from 10-1000 cells, with saturation of insulinsecretion beyond the critical size of about 100 cells, as apparent fromsome images after histology as shown in FIGS. 14A and 14B. Therefore,the architecture of cell aggregates within the transplant shouldoptimally mimic these natural size distributions of islets within ahealthy set of pancreas.

FIG. 15 illustrates an image of bio-printing system 1500, in accordancewith at least one example of the present disclosure. Bio-printing system1500 can include first dispenser 1502, second dispenser 1504, controller1506, printed material 1508, and sorting system 1510.

Sorting system 1510 can be any of the sorting systems described withrespect to the FIGS. above, such as system 1300 of FIG. 13. Sortingsystem 1510 can be connected to first dispenser 1502 and seconddispenser 1504, where first dispenser 1502 can receive, for example,large islets from sorting system 1510 and second dispenser 1504 canreceive, for example small islets from sorting system 1510. In someexamples, a third dispenser configured to receive medium sized isletsfrom sorting system 1510 can be included in bio-printing system 1502.

In some examples, first dispenser 1502 can be configured to dispense thesmall viable islets and second dispenser 1504 can be configured todispense large viable islets. Controller 1506 can be in communicationwith first dispenser 1502 and second dispenser 1504 to selectivelyoperate first dispenser 1502 and second dispenser 1504 to print thesmall viable islets and the large viable islets onto an implantablesubstrate.

In some examples, bio-printing system 1502 can include additionaldispensers configured to dispense additional material configured to aidin transplant and acceptance thereof by the recipient. In some examples,implant 1508 can receive stem cell aggregates that can improvevascularization of implant. In some other examples, implant 1508 canreceive angeogenic growth factors to activate receptors on endothelialcells. These methods can improve acceptance of the implant and can lowerrejection.

Bio-printing system 1500 can also provide a system for printingspatially patterned cell aggregates, or a size distribution of isletsthat can be required to attain normal functionality. In some examples,bio-printing system 1500 can modify the printed implant based on anatomy(such as body mass) of patient, which can further improve implantacceptance and can help prevent rejection.

VARIOUS NOTES & EXAMPLES

To further illustrate the apparatuses and systems disclosed herein, thefollowing non-limiting examples are provided:

Example 1 is a microfluidic device comprising: an upstream passageconfigured to provide a focusing stream; a sample passage configured toprovide a sample stream; a bifurcating passage including a specifiedbifurcating flow resistance; a combining passage configured to create acombined stream from the focusing stream and the sample stream, thefocusing stream directing the sample stream away from the upstreampassage and toward the bifurcating passage; wherein a first portion ofthe combined stream is discharged through the bifurcating passage; and amain discharge configured to discharge a second portion of the combinedstream, the main discharge including a main discharge resistance that isselectable to vary the main discharge resistance relative to thebifurcating flow resistance.

In Example 2, the subject matter of Example 1 optionally includes themain discharge further comprising: a main discharge multiplexerconfigured to selectively vary the main discharge resistance.

In Example 3, the subject matter of Example 2 optionally includes thebifurcating passage further comprising: a bifurcating passagemultiplexer configured to selectively vary the bifurcating passageresistance.

In Example 4, the subject matter of any one or more of Examples 1-3optionally include wherein: the upstream passage is configured todeliver the focusing stream to selectably determine a particle sizeaccepted by the bifurcating passage.

In Example 5, the subject matter of any one or more of Examples 1-4optionally include wherein: the upstream passage and the sample passageare configured to create a pinch width in the combining chamber todirect the sample stream towards the bifurcating passage.

In Example 6, the subject matter of Example 5 optionally includeswherein the upstream passage is configured to deliver the focusingstream at a laminar flow rate and the sample passage is configured todeliver the stream flow at a laminar flow rate.

Example 7 is a microfluidic system comprising: a sample passageconfigured to deliver a sample stream; a plurality of upstream passageseach configured to provide one of a plurality of focusing streams; aplurality of bifurcating passages, each of the plurality of bifurcatingpassages disposed downstream of one of the plurality of upstreampassages and configured to discharge a portion of the sample stream; anda plurality of combining passages, each of the plurality of combiningpassages configured to create a combined stream from one of theplurality of focusing streams and the sample stream, each of theplurality of focusing streams directing the sample stream away from theplurality of upstream passages and toward one of the bifurcatingpassages disposed downstream of the one of the upstream passages a maindischarge configured to discharge a second portion of the combinedstream.

In Example 8, the subject matter of Example 7 optionally includes themain discharge further comprising: a main discharge multiplexerconfigured to selectively vary a main discharge resistance.

In Example 9, the subject matter of Example 8 optionally includes abifurcating passage multiplexer coupled to each of the bifurcatingpassages, the bifurcating passage multiplexer configured to selectivelyvary a bifurcating passage resistance of each of the bifurcatingpassages.

In Example 10, the subject matter of Example 9 optionally includes amain discharge sensor coupled to the main discharge and configured toproduce a main discharge signal as a function of a sensed condition ofthe main discharge; a bifurcating passage manifold coupled to adischarge of each of the bifurcating passages; and a bifurcating passagesensor coupled to the bifurcating passage manifold and configured toproduce a bifurcating passage signal as a function of a sensed conditionof the bifurcating passage manifold.

In Example 11, the subject matter of Example 10 optionally includes acontroller configured to operate the main discharge multiplexer and thebifurcating passage multiplexer as a function of one or more of the maindischarge signal and the bifurcating passage signal.

In Example 12, the subject matter of any one or more of Examples 8-11optionally include wherein: each of the plurality of upstream passagesis configured to provide the focusing flow to create a selection widthupstream of each of the plurality of bifurcating passages.

Example 13 is a microfluidic sorting system comprising: a microfluidicdevice comprising: an upstream passage; a sample passage; a bifurcatingpassage comprising a specified bifurcating flow resistance; a maindischarge including a main discharge resistance that is selectable tovary the main discharge resistance relative to the bifurcating flowresistance.

In Example 14, the subject matter of Example 13 optionally includes abifurcating passage multiplexer configured to selectively vary thebifurcating passage resistance.

In Example 15, the subject matter of Example 14 optionally includes amain discharge sensor coupled to the main discharge and configured toproduce a main discharge signal as a function of a sensed condition ofthe main discharge.

In Example 16, the subject matter of Example 15 optionally includes abifurcating passage manifold coupled to a discharge of each of thebifurcating passages; and a bifurcating passage sensor coupled to thebifurcating passage manifold and configured to produce a bifurcatingpassage signal as a function of a sensed condition of the bifurcatingpassage manifold.

In Example 17, the subject matter of Example 16 optionally includeswherein: the controller is configured to select the main dischargeresistance and the bifurcating passage resistance as a function of atleast one of the main discharge signal and the bifurcating passagesignal.

In Example 18, the subject matter of any one or more of Examples 13-17optionally include wherein the controller is configured to select maindischarge resistance and the bifurcating passage resistance to: separateacinar from islets; separate large islets from small islets; andseparate viable islets from non-viable islets.

In Example 19, the subject matter of any one or more of Examples 13-18optionally include wherein the microfluidic device further comprises: aplurality of upstream passages each configured to provide one of aplurality of focusing streams; and a plurality of bifurcating passages,each of the plurality of bifurcating passages disposed downstream of oneof the plurality of upstream passages and configured to discharge aportion of the sample stream.

In Example 20, the subject matter of any one or more of Examples 13-19optionally include wherein the bifurcating passage comprises arestriction sized to be about 80 percent of a diameter of an acinardiameter.

Example 21 is a microfluidic sorting system comprising: a first sortingstage configured to perform hydrodynamic filtration to separate largeparticles from medium particles and small particles, the first sortingstage comprising a first stage first discharge and a first stage seconddischarge; and a second sorting stage connected to the first stage firstdischarge, the second sorting stage configured to perform two-cycleseparation to separate deformable large particles from non-deformablelarge particles.

In Example 22, the subject matter of Example 21 optionally includes athird sorting stage connected to the first stage second discharge, thethird sorting stage configured to perform hydrodynamic filtration toseparate medium particles from small particles, the third sorting stagecomprising a third stage first discharge and a third stage seconddischarge.

In Example 23, the subject matter of any one or more of Examples 21-22optionally include a fourth sorting stage connected to the third stagefirst discharge, the fourth sorting stage configured to performtwo-cycle separation to separate deformable medium particles fromnon-deformable medium particles; and a fifth sorting stage connected tothe third stage second discharge, the fifth sorting stage configured toperform crossflow filtration to separate deformable small particles fromnon-deformable small particles; the fifth sorting stage comprising afifth stage discharge; and a sixth sorting stage connected to the fifthstage discharge, the sixth sorting stage configured to perform two-cyclefiltration to separate first non-deformable small particles from secondnon-deformable small particles.

Example 24 is a bio-printing system comprising: a microfluidicseparating system configured to: separate acinar from islets; separatelarge islets from small islets; and separate viable islets fromnon-viable islets; a first dispenser configured to receive from smallviable islets from the microfluidic separation system and configured todispense the small viable islets; a second dispenser configured toreceive large viable islets from the microfluidic separation system andconfigured to dispense large viable islets; and a controller configuredto selectively operate the first dispenser and the second dispenser toprint the small viable islets and the large viable islets onto animplantable substrate.

In Example 25, the subject matter of Example 24 optionally includes themicrofluidic separating system further comprising: a sample passageconfigured to deliver a sample stream; a plurality of upstream passageseach configured to provide one of a plurality of focusing streams; aplurality of bifurcating passages, each of the plurality of bifurcatingpassages disposed downstream of one of the plurality of upstreampassages and configured to discharge a portion of the sample stream; anda plurality of combining passages, each of the plurality of combiningpassages configured to create a combined stream from one of theplurality of focusing streams and the sample stream, each of theplurality of focusing streams directing the sample stream away from theplurality of upstream passages and toward one of the bifurcatingpassages disposed downstream of the one of the upstream passages a maindischarge configured to discharge a second portion of the combinedstream.

In Example 26, the subject matter of any one or more of Examples 24-25optionally include the microfluidic separating system furthercomprising: a main discharge multiplexer configured to selectively varythe main discharge resistance; a bifurcating passage multiplexer coupledto each of the bifurcating passages, the bifurcating passage multiplexerconfigured to selectively vary a bifurcating passage resistance of eachof the bifurcating passages; a main discharge sensor in fluid coupled tothe main discharge and configured to produce a main discharge signal asa function of a sensed condition of the main discharge; a bifurcatingpassage manifold coupled to a discharge of each of the bifurcatingpassages; and a bifurcating passage sensor coupled to the bifurcatingpassage manifold and configured to produce a bifurcating passage signalas a function of a sensed condition of the bifurcating passage manifold.

In Example 27, the subject matter of any one or more of Examples 24-26optionally include a first sorting stage configured to performhydrodynamic filtration to separate large particles from mediumparticles and small particles, the first sorting stage comprising afirst stage first discharge and a first stage second discharge; and asecond sorting stage connected to the first stage first discharge, thesecond sorting stage configured to perform two-cycle separation toseparate large acinar particles from large islet particles.

In Example 28, the subject matter of Example 27 optionally includes athird sorting stage connected to the first stage second discharge, thethird sorting stage configured to perform hydrodynamic filtration toseparate medium particles from small particles, the third sorting stagecomprising a third stage first discharge and a third stage seconddischarge; a fourth sorting stage connected to the third stage firstdischarge, the fourth sorting stage configured to perform two-cycleseparation to separate medium acinar from medium islets; a fifth sortingstage connected to the third stage second discharge, the fifth sortingstage configured to perform crossflow filtration to separate smallacinar from small islets; the fifth sorting stage comprising a fifthstage discharge; and a sixth sorting stage connected to the fifth stagedischarge, the sixth sorting stage configured to perform two-cyclefiltration to separate non-viable small islets from viable small islets.

In Example 29, the microfluidic device, system, assembly, or method ofany one of or any combination of Examples 1-29 is optionally configuredsuch that all elements or options recited are available to use or selectfrom.

Each of these non-limiting examples can stand on its own, or can becombined in any permutation or combination with any one or more of theother examples.

The above detailed description includes references to the accompanyingdrawings, which form a part of the detailed description. The drawingsshow, by way of illustration, specific embodiments in which the presentsubject matter can be practiced. These embodiments are also referred toherein as “examples.” Such examples can include elements in addition tothose shown or described. However, the present inventors alsocontemplate examples in which only those elements shown or described areprovided. Moreover, the present inventors also contemplate examplesusing any combination or permutation of those elements shown ordescribed (or one or more aspects thereof), either with respect to aparticular example (or one or more aspects thereof), or with respect toother examples (or one or more aspects thereof) shown or describedherein.

In the event of inconsistent usages between this document and anydocuments so incorporated by reference, the usage in this documentcontrols.

In this document, the terms “a” or “an” are used, as is common in patentdocuments, to include one or more than one, independent of any otherinstances or usages of “at least one” or “one or more.” In thisdocument, the term “or” is used to refer to a nonexclusive or, such that“A or B” includes “A but not B,” “B but not A,” and “A and B,” unlessotherwise indicated. In this document, the terms “including” and “inwhich” are used as the plain-English equivalents of the respective terms“comprising” and “wherein.” Also, in the following claims, the terms“including” and “comprising” are open-ended, that is, a system, device,article, composition, formulation, or process that includes elements inaddition to those listed after such a term in a claim are still deemedto fall within the scope of that claim. Moreover, in the followingclaims, the terms “first,” “second,” and “third,” etc. are used merelyas labels, and are not intended to impose numerical requirements ontheir objects.

Method examples described herein can be machine or computer-implementedat least in part. Some examples can include a computer-readable mediumor machine-readable medium encoded with instructions operable toconfigure an electronic device to perform methods as described in theabove examples. An implementation of such methods can include code, suchas microcode, assembly language code, a higher-level language code, orthe like. Such code can include computer readable instructions forperforming various methods. The code may form portions of computerprogram products. Further, in an example, the code can be tangiblystored on one or more volatile, non-transitory, or non-volatile tangiblecomputer-readable media, such as during execution or at other times.Examples of these tangible computer-readable media can include, but arenot limited to, hard disks, removable magnetic disks, removable opticaldisks (e.g., compact disks and digital video disks), magnetic cassettes,memory cards or sticks, random access memories (RAMs), read onlymemories (ROMs), and the like.

The above description is intended to be illustrative, and notrestrictive. For example, the above-described examples (or one or moreaspects thereof) may be used in combination with each other. Otherembodiments can be used, such as by one of ordinary skill in the artupon reviewing the above description. The Abstract is provided to allowthe reader to quickly ascertain the nature of the technical disclosure.It is submitted with the understanding that it will not be used tointerpret or limit the scope or meaning of the claims. Also, in theabove Detailed Description, various features may be grouped together tostreamline the disclosure. This should not be interpreted as intendingthat an unclaimed disclosed feature is essential to any claim. Rather,inventive subject matter may lie in less than all features of aparticular disclosed embodiment. Thus, the following claims are herebyincorporated into the Detailed Description as examples or embodiments,with each claim standing on its own as a separate embodiment, and it iscontemplated that such embodiments can be combined with each other invarious combinations or permutations. The scope of the present subjectmatter should be determined with reference to the appended claims, alongwith the full scope of equivalents to which such claims are entitled.

1. A microfluidic device comprising: an upstream passage configured toprovide a focusing stream; a sample passage configured to provide asample stream; a bifurcating passage including a specified bifurcatingflow resistance; a combining passage configured to create a combinedstream from the focusing stream and the sample stream, the focusingstream directing the sample stream away from the upstream passage andtoward the bifurcating passage; wherein a first portion of the combinedstream is discharged through the bifurcating passage; and a maindischarge configured to discharge a second portion of the combinedstream, the main discharge including a main discharge resistance that isselectable to vary the main discharge resistance relative to thebifurcating flow resistance.
 2. The microfluidic device of claim 1, themain discharge further comprising: a main discharge multiplexerconfigured to selectively vary the main discharge resistance.
 3. Themicrofluidic device of claim 2, the bifurcating passage furthercomprising: a bifurcating passage multiplexer configured to selectivelyvary the bifurcating passage resistance.
 4. The microfluidic device ofclaim 1, wherein: the upstream passage is configured to deliver thefocusing stream to selectably determine a particle size accepted by thebifurcating passage.
 5. The microfluidic device of claim 1, wherein: theupstream passage and the sample passage are configured to create a pinchwidth in the combining chamber to direct the sample stream towards thebifurcating passage.
 6. The microfluidic device of claim 5, wherein theupstream passage is configured to deliver the focusing stream at alaminar flow rate and the sample passage is configured to deliver thestream flow at a laminar flow rate.
 7. A microfluidic system comprising:a sample passage configured to deliver a sample stream; a plurality ofupstream passages each configured to provide one of a plurality offocusing streams; a plurality of bifurcating passages, each of theplurality of bifurcating passages disposed downstream of one of theplurality of upstream passages and configured to discharge a portion ofthe sample stream; a plurality of combining passages, each of theplurality of combining passages configured to create a combined streamfrom one of the plurality of focusing streams and the sample stream,each of the plurality of focusing streams directing the sample streamaway from the plurality of upstream passages and toward one of thebifurcating passages disposed downstream of the one of the upstreampassages; and a main discharge configured to discharge a second portionof the combined stream.
 8. The microfluidic system of claim 7, the maindischarge further comprising: a main discharge multiplexer configured toselectively vary a main discharge resistance.
 9. The microfluidic systemof claim 8, further comprising: a bifurcating passage multiplexercoupled to each of the bifurcating passages, the bifurcating passagemultiplexer configured to selectively vary a bifurcating passageresistance of each of the bifurcating passages.
 10. The microfluidicsystem of claim 9, further comprising: a main discharge sensor coupledto the main discharge and configured to produce a main discharge signalas a function of a sensed condition of the main discharge; a bifurcatingpassage manifold coupled to a discharge of each of the bifurcatingpassages; and a bifurcating passage sensor coupled to the bifurcatingpassage manifold and configured to produce a bifurcating passage signalas a function of a sensed condition of the bifurcating passage manifold.11. The microfluidic system of claim 10, further comprising: acontroller configured to operate the main discharge multiplexer and thebifurcating passage multiplexer as a function of one or more of the maindischarge signal and the bifurcating passage signal.
 12. The system ofclaim 8, wherein: each of the plurality of upstream passages isconfigured to provide the focusing flow to create a selection widthupstream of each of the plurality of bifurcating passages.
 13. Amicrofluidic sorting system comprising: a microfluidic devicecomprising: an upstream passage; a sample passage; a bifurcating passagecomprising a specified bifurcating flow resistance; and a main dischargeincluding a main discharge resistance that is selectable to vary themain discharge resistance relative to the bifurcating flow resistance; amain discharge multiplexer configured to selectively vary the maindischarge resistance; and a controller configured to select the maindischarge resistance as a function of a condition of the microfluidicsorting system.
 14. The microfluidic sorting system of claim 13, furthercomprising: a bifurcating passage multiplexer configured to selectivelyvary the bifurcating passage resistance.
 15. The microfluidic sortingsystem of claim 14, further comprising: a main discharge sensor coupledto the main discharge and configured to produce a main discharge signalas a function of a sensed condition of the main discharge.
 16. Themicrofluidic sorting system of claim 15, further comprising: abifurcating passage manifold coupled to a discharge of each of thebifurcating passages; and a bifurcating passage sensor coupled to thebifurcating passage manifold and configured to produce a bifurcatingpassage signal as a function of a sensed condition of the bifurcatingpassage manifold.
 17. The microfluidic sorting system of claim 16,wherein: the controller is configured to select the main dischargeresistance and the bifurcating passage resistance as a function of atleast one of the main discharge signal and the bifurcating passagesignal.
 18. The microfluidic sorting system of claim 13, wherein thecontroller is configured to select main discharge resistance and thebifurcating passage resistance to: separate acinar from islets; separatelarge islets from small islets; and separate viable islets fromnon-viable islets.
 19. The microfluidic sorting system of claim 13,wherein the microfluidic device further comprises: a plurality ofupstream passages each configured to provide one of a plurality offocusing streams; and a plurality of bifurcating passages, each of theplurality of bifurcating passages disposed downstream of one of theplurality of upstream passages and configured to discharge a portion ofthe sample stream.
 20. The microfluidic sorting system of claim 13,wherein the bifurcating passage comprises a restriction sized to beabout 80 percent of a diameter of an acinar diameter.